Robert is a month shy of his fifth birthday, and a fistfight away from being expelled from junior kindergarten.

He trips, pinches and punches, and his teacher complains that he cannot work in a team or even on his own for very long. He is smart -- a recent test put his IQ at 148 -- but he is in danger of falling behind. One more misstep, his private school has warned, and he's gone. (At least until he is required to show up somewhere for class this fall.

"We thought he was just being boyish," says his mother.

"Imagine," sighs his father. "Expelled from junior K."

Educators see kids like Robert all the time: An estimated one in four children show up on that first day of school, short on the basic tools they need to succeed, from simple language to fine motor skills to co-operating with classmates.

Study after study shows that children who do not arrive "ready to learn" fall behind, are rejected by peers and sour on school, setting them on high-risk paths toward unhealthy, unhappy adulthoods.

Robert's troubles come as a shock to his attentive parents, a pair of PhDs with good jobs, a house full of books and a playroom cluttered with toys. If anything, they have been too doting on their firstborn. (They spoke only on the condition that their son's real name not be used.)

Until recently, even experts assumed that children headed for problems were easy to spot: They came from poor backgrounds, the offspring of drug addicts and alcoholics, abused and neglected by their parents.

It is just not that simple, and recent findings have bolstered criticism of Canada's early childhood policy, which has largely targeted low-income families.

Yes, money matters: Children who grow up in poverty are more likely to arrive unprepared for school than their financially better-off counterparts. But in real numbers, more than 60 per cent of vulnerable children in Canada are more thinly spread throughout the middle classes of the country, in families that look a lot like Robert's. They show up in comfortable two-parent homes, awash in Fisher Price and Playmobil, the brothers and sisters to scholastic stars.

A national study of 22,000 children from birth to age 11, using parental surveys and home visits, found that 37 per cent of children in the poorest families were vulnerable on one or more skill sets: They had difficult temperaments, limited communications skills or below-average physical abilities.

But even among Canada's wealthiest families -- the top quarter of earners -- almost one in four children (24 per cent) were also flagged with problems.

A second study evaluated every kindergarten student in the city of Vancouver and reached the same conclusion: True, the proportion of children with school-readiness shortfalls increased dramatically as one moved from the most affluent west-side neighbourhoods to the poorest east-end parts of the city. But the largest number of vulnerable children were spread through the city's middle-class sections.

"This is a vitally important story," said Clyde Hertzman, the University of British Columbia researcher who is now mapping the entire province. "The numbers game [says]that if you concentrate all your energy in the least-advantaged group, then you miss the majority of kids who are developmentally delayed. These are issues that apply, one way or another, across society."

Jim Grieves, the director of education for the Peel School Board, remembers from his days as a school principal the students who arrived in designer clothes but without consistent parental support. Now, when he presents the statistics to middle-class audiences, their first reaction is to "rail against" them.

"We're raised on the notion that if you have money and advantage, you can pretty much assume everything will turn out fine," he said. "But then they assess the pace of life, and the way they are struggling to maintain even middle-class status, and they see there are lots of holes in the way we are raising our children. It's pretty scary, actually."

Of course, the majority of children in Canada are raised in middle-class families, so it might seem natural that most of the children at risk would come from their ranks. But the findings toppled a long-standing hypothesis. Experts and government officials expected to find a mass of children with problems clustered among poor Canadians, and the offspring of the middle class doing fine and looking pretty similar to each other, apart from the luck of genes and IQ.